Fluid-storing material



Patented Mar. 19, 1929.

unirso stares Parana" Fries.

FREDERICK G. KEYES, OF CAMBRIDGE, MASSACHUSETTS, ASSIGNOR, BY MESNE .AS SIGNMENTS, TO NATIONAL REFRIGERATING COMPANY, OF BOSTON, MASSACHU- SETTS, A CORPORATION OF MASSACHUSETTS.

FLUID-STORING MATERIAL.

No Drawing; Original application filed September 26, 1922, Serial No. 590,668 Divided and this application filed November 6, 1923. Serial No. 673,104.

The present invention relates to improvements in gas or liquid storing materials useful in the arts generally and particularly in refrigerating apparatus, one form of such an apparatus being shown in my application for atent for refrigeration, filed June 8, 1921, erial N o. 47 5,855, of which this application is a continuation in part. This application is a division of my application, Serial No.

590,668, filed September 26, 1922.

By Way of example, the liquid or gas to be stored is referred to hereinafter as a refrigerant, such as ammonia, which is commonly used in refrigerating apparatus although it is to be understood that my invention is not limited to the use of this particular fluid or to refrigerating apparatus.

The storing material in a still is an important element in a refrigerator apparatus and should preferably be a solid material capable of taking up the refrigerant and holding it in such a physical state as to maintain its vapor pressure below that ofthe free liquid. Several important factors'enter into the production of a practical and highly efficient storing material to be used in a safe refrigerator apparatus, and the desirable properties or qualities of such a material are:

lQIt must be stable at elevated temperatures;

2. It must not react under any conditions of use with the metal used to contain it;

'3. The unit weight of the material must take up a large amount of refrigerant;

4. Its heat capacity must be as small as possible; and,

5. It must be brought into such a physical state of the addition of cementitious substances and preferred physical and chemical treatment as to remain under use in the form of discreet hard and porous granules capable of presenting a large surface for ready speedy absorption of the refrigerant, this being a eration.

It is evident in selecting a cementitious substance designed to' confer the property of hardness in the grains of the final storing material that the chosen cements or cementing compounds retain their property at high temperatures to which on occasion the gas storing material may be exposed.

I have found that by special treatment of cellular material, such as charcoal, with certain metallic salts, for example, zinc chloride, ChI'OlIllC acid, etc., a substance is produced which I term activated charcoal and one well suited as a storing material for use in refrigerating apparatus. This material condenses the refrigerant on its surfaces, hold- .ing it with great tenacity at room temperature, and readily and completely giving it up at moderately elevated temperatures, 150 C. The use of activated charcoal as a storing material in refrigerating machines, due to its large bulk per unit weight necessitates a large still which in turn offers a large surface for radiation involving a possible diminution in the efliciency of operation of the apparatus, as compared With the efficiencies obtainable when other materials are used. Moreover, because of the small specific quantity of refrigerant taken up much energy is lost in heating the charcoal. The great advantage, however, of an absorbent such as charcoal is that it takes up the refrigerant with extreme rapidity and this is an advantage at the end of the distillation period when it is necessary to start the return of the refrigerant promptly fromthe refrigerating chamber. For example, one gram of charcoal in its optimum state of activity has a heat capacity of about .25 calories per gram. The maximum amount of ammonia, for example, which a certain sample will take up is, for example, 0.125 and the heat necessary to drive this-01f at 150 C. is about 75calories. In heating to 150 0. therefore, about 38 calories are used up owing to the heat capacity of the absorbent material so that 26 per cent of the energy has been thrown away on heating. the material. It is clear therefore that an increase in efficiency would be obtained if less heat were necessary to disengage the gas from the storing material and less heat were necessary to raise the material to the point Where the refrigerant is given up. In the case of other absorbing substances such as silica gel or metallic oxide gels the same general state of fn ct obtains as for charcoal or carbon in the absorbing state. A variety of substances were considered as storing materials for refrigerating machines and calcium chloride settled upon as the most feasible material. Each gram of the last named substance takes up 1.22 grams of ammonia and the ammonia moreover enters into chemical combinations as stated in the formula CaCl .8NI-I,. lhere are "other calcium chloride compounds, one said to contain 4 molecules of ammonia, but the formula given corresponds to the maximum amount of ammonia and moreover possesse s a very small. pressure of ammonia at ordinary temperature. It was found in using this material alone that the rate'at which it would take up ammonia was very small due to a tendency to pulverize and to pack, thus preventing ready access of the refrigerant.

It became, therefore, a problem of discover-. ing the best physical state and mode of preparation of this materialso as to maintain it in the still under the conditions of operation in such a state that it would expose the maximum surface and remain in a hard, durable 'yet porous condition offering .no resistance to the free circulation of the refri erant among the granules of the absor ent. It was found that Portland cement mixed with the chloride to the amount of 10 to 15 per cent and sufficient water to form a thick paste could be slowly baked in the .presence of ammonia so as to give a material in hard porous grains which maintained their form 'under repeated heating and coollng 1n the distilling and taking up of the ammonia.

This material, however, while serviceable may develop a tendency, due to its composition, to dehydrate, when operated at extremely elevated temperatures.

It has been known for a long time that zinc chloride forms with zinc oxide certain oxychlorides and also that magnesium chloride forms with magnesium oxide similar oxychlorides which are in effect hard cements. Moreover, it is a fact of common observation that sodium silicate will, upon heating, blow up-to a porous, spongy mass. I'make use of the above mentioned characteristics of these substances to produce a hard porous storing materialfor refrigerant gases and liquids having a large taking up capacity together with a high rate of taking up, the physical structure being such as to persist and withstand the disintegrating action of rapid heating and cooling and changes of volume pro duced by taking up and disengaging refrigerant, as follows Dry calcium chloride is mixed with 10 per cent of molecular proportionsdry zinc oxide (ZnO) and zinc chloride (ZnCl or is mixed with 10 per cent of molecular proportions of dry magnesium oxide (M and magnesium chloride (M C1 r fter thorough incorporation in a ba 1 mill the selected mixture is then moistened with sodium silicate or other alkali metal silicate such as potassium or even berrilium silicate (in sufficient amount that there will be 3 per cent silicate in the mixture. when dry) and the pasty mass dried first in a current of air at about 250 C. The material is then broken up and sifted and then treated at 500 to 600 C. in the presence when cooled and readilyv giving it up when I heated to a temperature of about 150 0., a smaller containing still is used in the ap paratus than when activated charcoal alone is used as the storing material therein, and the radiation losses at the still of the apparatus are therefore minimized. The described material has been used alone in a commercially operating machine. .I have found, also, by mixing approximately equal volumes of activated charcoal and one or the other of the above mentioned calcium chloride mixtures in a small still, the charcoal serving to support and to maintain even distribution of the chloride mixture throughout the still and aiding to promptly start the refrigerating period due to the extreme speed with which it takes up the refrigerant, that highly eflicient operation of the apparatus is obtained.

What I claim is 1. A porous storing material for gases and liquids comprising calcium chloride qualified by magnesium oxychloride, and activated charcoal.

2. A storing material for gases and liquidscomprising 'a granular absorbent material and activated charcoal.

3. A storing material for gases and li uids comprising a granular chemical absor ent material and activated charcoal.

In testimony whereof I hereto aflix my signature.

FREDERICK e. KEYES. 

